Method of Measuring Overlay Error and a Device Manufacturing Method

ABSTRACT

The overlay error of a target in a scribelane is measured. The overlay error of the required feature in the chip area may differ from this due to, for example, different responses to the exposure process. A model is used to simulate these differences and thus a more accurate measurement of the overlay error of the feature determined.

This application incorporates by reference in their entireties U.S.application Ser. No. 13/055,594 and U.S. Provisional Appl. No.61/090,118.

FIELD

The present invention relates to methods of inspection usable, forexample, in the manufacture of devices by lithographic techniques and tomethods of manufacturing devices using lithographic techniques.

BACKGROUND

A lithographic apparatus is a machine that applies a desired patternonto a substrate, usually onto a target portion of the substrate. Alithographic apparatus can be used, for example, in the manufacture ofintegrated circuits (ICs). In that instance, a patterning device, whichis alternatively referred to as a mask or a reticle, may be used togenerate a circuit pattern to be formed on an individual layer of theIC. This pattern can be transferred onto a target portion (e.g.,comprising part of, one, or several dies) on a substrate (e.g., asilicon wafer). Transfer of the pattern is typically via imaging onto alayer of radiation-sensitive material (resist) provided on thesubstrate. In general, a single substrate will contain a network ofadjacent target portions that are successively patterned. Knownlithographic apparatus include so-called steppers, in which each targetportion is irradiated by exposing an entire pattern onto the targetportion at one time, and so-called scanners, in which each targetportion is irradiated by scanning the pattern through a radiation beamin a given direction (the “scanning”-direction) while synchronouslyscanning the substrate parallel or anti-parallel to this direction. Itis also possible to transfer the pattern from the patterning device tothe substrate by imprinting the pattern onto the substrate.

In order to monitor the lithographic process, it is necessary to measureparameters of the patterned substrate, for example the overlay errorbetween successive layers formed in or on it. There are varioustechniques for making measurements of the microscopic structures formedin lithographic processes, including the use of scanning electronmicroscopes and various specialized tools. One form of specializedinspection tool is a scatterometer in which a beam of radiation isdirected onto a target on the surface of the substrate, and propertiesof the scattered or reflected beam are measured. By comparing theproperties of the beam before and after it has been reflected orscattered by the substrate, the properties of the substrate can bedetermined. This can be done, for example, by comparing the reflectedbeam with data stored in a library of known measurements associated withknown substrate properties. Two main types of scatterometer are known.Spectroscopic scatterometers direct a broadband radiation beam onto thesubstrate, and measure the spectrum (intensity as a function ofwavelength) of the radiation scattered into a particular narrow angularrange. Angularly resolved scatterometers use a monochromatic radiationbeam and measure the intensity of the scattered radiation as a functionof angle.

Measurement of the overlay error is generally achieved by etchingspecific targets in an unused area of the substrate, known as ascribelane. The overlay error of all the relevant features is thenassumed to be the same as the measured overlay error of the target in anearby scribelane. However, the true overlay error of a particularfeature may be affected by a number of different factors, and thus maynot be the same as the overlay error of the designated target in thescribelane. In particular, overlay targets may have a different responseto changes in illumination mode, polarization and aberrations (staticand dynamic) from the feature to measured. Additionally the scribelanemay not be very close to the particular feature concerned and thus someinterpolation between neighboring targets may be necessary. Furthermore,the process dependencies used of the feature and the target may bedifferent due to different geometry and surrounding structures.

SUMMARY

It is desirable to provide a method which more accurately determines theoverlay error of a feature of interest based on measuring overlay fromdedicated targets.

According to an embodiment of the invention, there is provided a methodof determining overlay error of a feature exposed on a substrate by alithographic apparatus comprising the following steps. Measuring theoverlay error of a target. Determining the overlay error of the featurebased on the overlay error of the target and a model of lithographicapparatus metrology.

According to another embodiment of the invention, there is provided amethod of determining the overlay error of a feature exposed on asubstrate by a lithographic apparatus comprising the following steps.Measuring the overlay error of a target. Determining the overlay errorof the feature based on the overlay error of the target and a model, themodel modeling the relative overlay error at different positions on thesubstrate based on inputs from a substrate and/or the lithographicapparatus metrology.

According to a further embodiment of the invention, there is provided amethod of determining the overlay error of a feature on a substratecomprising the following steps. Measuring the overlay error of a target.Determining the overlay error of the feature based on the overlay errorof the target and a model, the model modeling the characteristics of thefeature.

According to a still further embodiment of the invention, there isprovided a lithographic apparatus to form a pattern on a substrate thatis configured to determine the overlay error using one or more of themethods as described above.

Further features and advantages of the invention, as well as thestructure and operation of various embodiments of the invention, aredescribed in detail below with reference to the accompanying drawings.It is noted that the invention is not limited to the specificembodiments described herein. Such embodiments are presented herein forillustrative purposes only. Additional embodiments will be apparent topersons skilled in the relevant art(s) based on the teachings containedherein.

BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES

The accompanying drawings, which are incorporated herein and form partof the specification, illustrate the present invention and, togetherwith the description, further serve to explain the principles of theinvention and to enable a person skilled in the relevant art(s) to makeand use the invention.

FIGS. 1A and 1B respectively depict reflective and transmissivelithographic apparatuses.

FIG. 2 depicts a lithographic cell or cluster.

FIG. 3 depicts an exemplary scatterometer.

FIG. 4 depicts another exemplary scatterometer.

FIG. 5 is a flow chart depicting a method.

The features and advantages of the present invention will become moreapparent from the detailed description set forth below when taken inconjunction with the drawings, in which like reference charactersidentify corresponding elements throughout. In the drawings, likereference numbers generally indicate identical, functionally similar,and/or structurally similar elements. The drawing in which an elementfirst appears is indicated by the leftmost digit(s) in the correspondingreference number.

DETAILED DESCRIPTION

This specification discloses one or more embodiments that incorporatethe features of this invention. The disclosed embodiment(s) merelyexemplify the invention. The scope of the invention is not limited tothe disclosed embodiment(s). The invention is defined by the claimsappended hereto.

The embodiment(s) described, and references in the specification to “oneembodiment”, “an embodiment”, “an example embodiment”, etc., indicatethat the embodiment(s) described may include a particular feature,structure, or characteristic, but every embodiment may not necessarilyinclude the particular feature, structure, or characteristic. Moreover,such phrases are not necessarily referring to the same embodiment.Further, when a particular feature, structure, or characteristic isdescribed in connection with an embodiment, it is understood that it iswithin the knowledge of one skilled in the art to effect such feature,structure, or characteristic in connection with other embodimentswhether or not explicitly described.

Embodiments of the invention may be implemented in hardware, firmware,software, or any combination thereof. Embodiments of the invention mayalso be implemented as instructions stored on a machine-readable medium,which may be read and executed by one or more processors. Amachine-readable medium may include any mechanism for storing ortransmitting information in a form readable by a machine (e.g., acomputing device). For example, a machine-readable medium may includeread only memory (ROM); random access memory (RAM); magnetic diskstorage media; optical storage media; flash memory devices; electrical,optical, acoustical or other forms of propagated signals (e.g., carrierwaves, infrared signals, digital signals, etc.), and others. Further,firmware, software, routines, instructions may be described herein asperforming certain actions. However, it should be appreciated that suchdescriptions are merely for convenience and that such actions in factresult from computing devices, processors, controllers, or other devicesexecuting the firmware, software, routines, instructions, etc.

FIGS. 1A and 1B schematically depict lithographic apparatus 100 andlithographic apparatus 100′, respectively. Lithographic apparatus 100and lithographic apparatus 100′ each include: an illumination system(illuminator) IL configured to condition a radiation beam B (e.g., DUVor EUV radiation); a support structure (e.g., a mask table) MTconfigured to support a patterning device (e.g., a mask, a reticle, or adynamic patterning device) MA and connected to a first positioner PMconfigured to accurately position the patterning device MA; and asubstrate table (e.g., a wafer table) WT configured to hold a substrate(e.g., a resist coated wafer) W and connected to a second positioner PWconfigured to accurately position the substrate W. Lithographicapparatuses 100 and 100′ also have a projection system PS configured toproject a pattern imparted to the radiation beam B by patterning deviceMA onto a target portion (e.g., comprising one or more dies) C of thesubstrate W. In lithographic apparatus 100 the patterning device MA andthe projection system PS is reflective, and in lithographic apparatus100′ the patterning device MA and the projection system PS istransmissive.

The illumination system IL may include various types of opticalcomponents, such as refractive, reflective, magnetic, electromagnetic,electrostatic or other types of optical components, or any combinationthereof, for directing, shaping, or controlling the radiation B.

The support structure MT holds the patterning device MA in a manner thatdepends on the orientation of the patterning device MA, the design ofthe lithographic apparatuses 100 and 100′, and other conditions, such asfor example whether or not the patterning device MA is held in a vacuumenvironment. The support structure MT may use mechanical, vacuum,electrostatic or other clamping techniques to hold the patterning deviceMA. The support structure MT may be a frame or a table, for example,which may be fixed or movable, as required. The support structure MT mayensure that the patterning device is at a desired position, for examplewith respect to the projection system PS.

The term “patterning device” MA should be broadly interpreted asreferring to any device that may be used to impart a radiation beam Bwith a pattern in its cross-section, such as to create a pattern in thetarget portion C of the substrate W. The pattern imparted to theradiation beam B may correspond to a particular functional layer in adevice being created in the target portion C, such as an integratedcircuit.

The patterning device MA may be transmissive (as in lithographicapparatus 100′ of FIG. 1B) or reflective (as in lithographic apparatus100 of FIG. 1A). Examples of patterning devices MA include reticles,masks, programmable mirror arrays, and programmable LCD panels. Masksare well known in lithography, and include mask types such as binary,alternating phase shift, and attenuated phase shift, as well as varioushybrid mask types. An example of a programmable mirror array employs amatrix arrangement of small mirrors, each of which may be individuallytilted so as to reflect an incoming radiation beam in differentdirections. The tilted mirrors impart a pattern in the radiation beam Bwhich is reflected by the mirror matrix.

The term “projection system” PS may encompass any type of projectionsystem, including refractive, reflective, catadioptric, magnetic,electromagnetic and electrostatic optical systems, or any combinationthereof, as appropriate for the exposure radiation being used, or forother factors, such as the use of an immersion liquid or the use of avacuum. A vacuum environment may be used for EUV or electron beamradiation since other gases may absorb too much radiation or electrons.A vacuum environment may therefore be provided to the whole beam pathwith the aid of a vacuum wall and vacuum pumps.

Lithographic apparatus 100 and/or lithographic apparatus 100′ may be ofa type having two (dual stage) or more substrate tables (and/or two ormore mask tables) WT. In such “multiple stage” machines the additionalsubstrate tables WT may be used in parallel, or preparatory steps may becarried out on one or more tables while one or more other substratetables WT are being used for exposure.

Referring to FIGS. 1A and 1B, the illuminator IL receives a radiationbeam from a radiation source SO. The source SO and the lithographicapparatuses 100, 100′ may be separate entities, for example when thesource SO is an excimer laser. In such cases, the source SO is notconsidered to form part of the lithographic apparatuses 100 or 100′, andthe radiation beam B passes from the source SO to the illuminator ILwith the aid of a beam delivery system BD (FIG. 1B) comprising, forexample, suitable directing mirrors and/or a beam expander. In othercases, the source SO may be an integral part of the lithographicapparatuses 100, 100′—for example when the source SO is a mercury lamp.The source SO and the illuminator IL, together with the beam deliverysystem BD, if required, may be referred to as a radiation system.

The illuminator IL may comprise an adjuster AD (FIG. 1B) for adjustingthe angular intensity distribution of the radiation beam. Generally, atleast the outer and/or inner radial extent (commonly referred to asσ-outer and σ-inner, respectively) of the intensity distribution in apupil plane of the illuminator may be adjusted. In addition, theilluminator IL may comprise various other components (FIG. 1B), such asan integrator IN and a condenser CO. The illuminator IL may be used tocondition the radiation beam B, to have a desired uniformity andintensity distribution in its cross section.

Referring to FIG. 1A, the radiation beam B is incident on the patterningdevice (e.g., mask) MA, which is held on the support structure (e.g.,mask table) MT, and is patterned by the patterning device MA. Inlithographic apparatus 100, the radiation beam B is reflected from thepatterning device (e.g., mask) MA. After being reflected from thepatterning device (e.g., mask) MA, the radiation beam B passes throughthe projection system PS, which focuses the radiation beam B onto atarget portion C of the substrate W. With the aid of the secondpositioner PW and position sensor IF2 (e.g., an interferometric device,linear encoder or capacitive sensor), the substrate table WT may bemoved accurately, e.g., so as to position different target portions C inthe path of the radiation beam B. Similarly, the first positioner PM andanother position sensor IF1 may be used to accurately position thepatterning device (e.g., mask) MA with respect to the path of theradiation beam B. Patterning device (e.g., mask) MA and substrate W maybe aligned using mask alignment marks M1, M2 and substrate alignmentmarks P1, P2.

Referring to FIG. 1B, the radiation beam B is incident on the patterningdevice (e.g., mask MA), which is held on the support structure (e.g.,mask table MT), and is patterned by the patterning device. Havingtraversed the mask MA, the radiation beam B passes through theprojection system PS, which focuses the beam onto a target portion C ofthe substrate W. With the aid of the second positioner PW and positionsensor IF (e.g., an interferometric device, linear encoder or capacitivesensor), the substrate table WT can be moved accurately, e.g., so as toposition different target portions C in the path of the radiation beamB. Similarly, the first positioner PM and another position sensor (whichis not explicitly depicted in FIG. 1B) can be used to accuratelyposition the mask MA with respect to the path of the radiation beam B,e.g., after mechanical retrieval from a mask library, or during a scan.

In general, movement of the mask table MT may be realized with the aidof a long-stroke module (coarse positioning) and a short-stroke module(fine positioning), which form part of the first positioner PM.Similarly, movement of the substrate table WT may be realized using along-stroke module and a short-stroke module, which form part of thesecond positioner PW. In the case of a stepper (as opposed to a scanner)the mask table MT may be connected to a short-stroke actuator only, ormay be fixed. Mask MA and substrate W may be aligned using maskalignment marks M1, M2 and substrate alignment marks P1, P2. Althoughthe substrate alignment marks as illustrated occupy dedicated targetportions, they may be located in spaces between target portions (knownas scribe-lane alignment marks). Similarly, in situations in which morethan one die is provided on the mask MA, the mask alignment marks may belocated between the dies.

The lithographic apparatuses 100 and 100′ may be used in at least one ofthe following modes:

1. In step mode, the support structure (e.g., mask table) MT and thesubstrate table WT are kept essentially stationary, while an entirepattern imparted to the radiation beam B is projected onto a targetportion C at one time (i.e., a single static exposure). The substratetable WT is then shifted in the X and/or Y direction so that a differenttarget portion C may be exposed.

2. In scan mode, the support structure (e.g., mask table) MT and thesubstrate table WT are scanned synchronously while a pattern imparted tothe radiation beam B is projected onto a target portion C (i.e., asingle dynamic exposure). The velocity and direction of the substratetable WT relative to the support structure (e.g., mask table) MT may bedetermined by the (de-)magnification and image reversal characteristicsof the projection system PS.

3. In another mode, the support structure (e.g., mask table) MT is keptsubstantially stationary holding a programmable patterning device, andthe substrate table WT is moved or scanned while a pattern imparted tothe radiation beam B is projected onto a target portion C. A pulsedradiation source SO may be employed and the programmable patterningdevice is updated as required after each movement of the substrate tableWT or in between successive radiation pulses during a scan. This mode ofoperation may be readily applied to maskless lithography that utilizesprogrammable patterning device, such as a programmable mirror array of atype as referred to herein.

Combinations and/or variations on the described modes of use or entirelydifferent modes of use may also be employed.

In a further embodiment, lithographic apparatus 100 includes an extremeultraviolet (EUV) source, which is configured to generate a beam of EUVradiation for EUV lithography. In general, the EUV source is configuredin a radiation system, and a corresponding illumination system isconfigured to condition the EUV radiation beam of the EUV source.

Combinations and/or variations on the above described modes of use orentirely different modes of use may also be employed.

As shown in FIG. 2, the lithographic apparatus LA forms part of alithographic cell LC, also sometimes referred to a lithocell or cluster,which also includes apparatus to perform pre- and post-exposureprocesses on a substrate. IN one example, a lithocell or cluster mayinclude spin coaters SC to deposit resist layers, developers DE todevelop exposed resist, chill plates CH and bake plates BK. A substratehandler, or robot, RO picks up substrates from input/output ports I/O1,I/O2, moves them between the different process apparatus and deliversthen to the loading bay LB of the lithographic apparatus. These devices,which are often collectively referred to as the track, are under thecontrol of a track control unit TCU, which is itself controlled by thesupervisory control system SCS, which also controls the lithographicapparatus via lithography control unit LACU. Thus, the differentapparatus can be operated to maximize throughput and processingefficiency.

In one example, it is desirable to inspect exposed substrates to measureproperties such as overlay errors between subsequent layers, linethicknesses, critical dimensions (CD), etc. If errors are detected,adjustments may be made to exposures of subsequent substrates,especially if the inspection can be done soon and fast enough that othersubstrates of the same batch are still to be exposed. Also, alreadyexposed substrates may be stripped and reworked, e.g., to improve yield,or discarded, thereby avoiding performing exposures on substrates thatare known to be faulty. In a case where only some target portions of asubstrate are faulty, further exposures can be performed only on thosetarget portions which are good.

An inspection apparatus is used to determine the properties of thesubstrates, and in particular, how the properties of differentsubstrates or different layers of the same substrate vary from layer tolayer. The inspection apparatus may be integrated into the lithographicapparatus LA or the lithocell LC or may be a stand-alone device. Toenable most rapid measurements, it is desirable that the inspectionapparatus measure properties in the exposed resist layer immediatelyafter the exposure. However, the latent image in the resist may have avery low contrast, i.e., there is only a very small difference inrefractive index between the parts of the resist which have been exposedto radiation and those which have not, and not all inspection apparatushave sufficient sensitivity to make useful measurements of the latentimage. Therefore, measurements may be taken after the post-exposure bakestep (PEB), which is customarily the first step carried out on exposedsubstrates and increases the contrast between exposed and unexposedparts of the resist. At this stage, the image in the resist may bereferred to as semi-latent. It is also possible to make measurements ofthe developed resist image, at which point either the exposed orunexposed parts of the resist have been removed, or after a patterntransfer step, such as etching. The latter possibility limits thepossibilities for rework of faulty substrates, but may still provideuseful information.

FIG. 3 depicts a scatterometer SM1 according to an embodiment of thepresent invention. It comprises a broadband (e.g., white light)radiation projector 2 that projects radiation onto a substrate W. Thereflected radiation is passed to a spectrometer detector 4, whichmeasures a spectrum 10 (e.g., intensity as a function of wavelength) ofthe specular reflected radiation. From this data, the structure orprofile giving rise to the detected spectrum may be reconstructed byprocessing unit PU, e.g., by Rigorous Coupled Wave Analysis andnon-linear regression or by comparison with a library of simulatedspectra, as shown at the bottom of FIG. 3. In one example, for thereconstruction the general form of the structure is known and someparameters are assumed from knowledge of the process by which thestructure was made, leaving only a few parameters of the structure to bedetermined from the scatterometry data. Such a scatterometer may beconfigured as, for example, a normal-incidence scatterometer or anoblique-incidence scatterometer.

FIG. 4 shows another scatterometer SM2 according to another embodimentof the present invention. In this device, the radiation emitted byradiation source 2 is focused using lens system 12 through interferencefilter 13 and polarizer 17, reflected by partially reflected surface 16,and is focused onto substrate W via a microscope objective lens 15,which has a high numerical aperture (NA), for example at least about 0.9or at least about 0.95. In some examples, immersion scatterometers mayeven have lenses with numerical apertures over about 1. The reflectedradiation then transmits through partially reflective surface 16 into adetector 18 in order to have the scatter spectrum detected. The detectormay be located in the back-projected pupil plane 11, which is at thefocal length of the lens system 15, however the pupil plane may insteadbe re-imaged with auxiliary optics (not shown) onto the detector 18. Forexample, the pupil plane is the plane in which the radial position ofradiation defines the angle of incidence and the angular positiondefines azimuth angle of the radiation. In one example, the detector isa two-dimensional detector so that a two-dimensional angular scatterspectrum of a substrate target 30 can be measured. The detector 18 maybe, for example, an array of CCD or CMOS sensors, and may use anintegration time of, for example, about 40 milliseconds per frame.

Additionally, or alternative, a reference beam is often used, forexample, to measure the intensity of the incident radiation. To do this,when the radiation beam is incident on the beam splitter 16, part of itis transmitted through the beam splitter as a reference beam towards areference mirror 14. The reference beam is then projected onto adifferent part of the same detector 18.

Additionally, or alternatively, a set of interference filters 13 isavailable to select a wavelength of interest in the range of, forexample, about 405-790 nm or even lower, such as about 200-300 nm. Theinterference filter may be tunable rather than comprising a set ofdifferent filters. A grating could be used instead of interferencefilters.

The detector 18 may measure the intensity of scattered light at a singlewavelength (or narrow wavelength range), the intensity separately atmultiple wavelengths or integrated over a wavelength range. Furthermore,the detector may separately measure the intensity of transversemagnetic- and transverse electric-polarized light and/or the phasedifference between the transverse magnetic- and transverseelectric-polarized light.

In one example, using a broadband light source (i.e., one with a widerange of light frequencies or wavelengths—and therefore of colors) ispossible, which gives a large etendue, allowing the mixing of multiplewavelengths. The plurality of wavelengths in the broadband each has abandwidth of *8 and a spacing of at least 2*8 (i.e., twice thebandwidth). Several “sources” of radiation can be different portions ofan extended radiation source which have been split using fiber bundles.In this way, angle resolved scatter spectra can be measured at multiplewavelengths in parallel. A 3-D spectrum (wavelength and two differentangles) can be measured, which contains more information than a 2-Dspectrum. This allows more information to be measured which increasesmetrology process robustness. This is described in more detail inEP1,628,164A, which is incorporated by reference herein in its entirety.

In one example, the target 30 on substrate W may be a grating, which isprinted such that after development, the bars are formed of solid resistlines. The bars may alternatively be etched into the substrate. Thispattern is sensitive to chromatic aberrations in the lithographicprojection apparatus, particularly the projection system PL, andillumination symmetry and the presence of such aberrations will manifestthemselves in a variation in the printed grating. Accordingly, thescatterometry data of the printed gratings is used to reconstruct thegratings. The parameters of the grating, such as line widths and shapes,may be input to the reconstruction process, performed by processing unitPU, from knowledge of the printing step and/or other scatterometryprocesses.

FIG. 5 shows a flowchart depicting a method to measure an overlay error.First, an overlay error of a substrate may be measured. From this value,the overlay error of a feature is calculated. However, a number offactors may mean that the overlay error of a feature is not the same asthe overlay error of a target.

Firstly, the process of exposing the substrate, including both thefeature and the target may itself yield variations in the overlay errorbetween the feature and the target, due to different responses to theillumination mode, polarization and aberrations. This may include, forexample, different inputs from the mask MA.

In step S1, an overlay error of a target is measured.

In step S2, a model is used to simulate any relative difference betweenthe overlay error of a feature and the overlay error of the target. Invarious examples, the model can be generated either by usinglithographic apparatus metrology, such as by taking aberrationmeasurements and accounting for the illumination mode and polarizationstate, or alternatively by using a test substrate to measure therelative differences due to these factors.

Secondly, the different locations of the feature and the target may alsoyield variations in the overlay error between the feature and thetarget. In step S3, a model is again used to simulate any relativedifferences due to the location of the feature and target. Again, invarious examples, this model can be generated either by using metrologydata from the lithographic apparatus and the mask or by using a testsubstrate to measure the relative differences due to these factors.

Thirdly, differences between the feature structure and characteristicsand the target structure and characteristics could result in differentoverlay errors due to the processing of the substrate, such as etching,deposition or polishing. These may be assessed using theoreticalresults, prior experience and/or databases. Alternatively, to assess thedifferent effects, the overlay error for a sample feature can bemeasured and compared to the overlay error for a target. In step S4,this is then used to model the difference in overlay error calculationsbetween the feature and the target due to product structure andcharacteristics.

If there are multiple features of interest on a substrate, differentmodels may be used for each feature to account for the differentlocations and different structures used. Furthermore the overlay errormay vary over time and this factor may be included in the model(s).

It is to be appreciated that to ensure the continued accuracy of thismethod over time, test substrates may be measured at regular andfrequent intervals so that the models account for any changes in theapparatus and process over time.

Although specific reference may be made in this text to the use oflithographic apparatus in the manufacture of ICs, it should beunderstood that the lithographic apparatus described herein may haveother applications, such as the manufacture of integrated opticalsystems, guidance and detection patterns for magnetic domain memories,flat-panel displays, liquid-crystal displays (LCDs), thin film magneticheads, etc. The skilled artisan will appreciate that, in the context ofsuch alternative applications, any use of the terms “wafer” or “die”herein may be considered as synonymous with the more general terms“substrate” or “target portion”, respectively. The substrate referred toherein may be processed, before or after exposure, in for example atrack (a tool that typically applies a layer of resist to a substrateand develops the exposed resist), a metrology tool and/or an inspectiontool. Where applicable, the disclosure herein may be applied to such andother substrate processing tools. Further, the substrate may beprocessed more than once, for example in order to create a multi-layerIC, so that the term substrate used herein may also refer to a substratethat already contains multiple processed layers.

Although specific reference may have been made above to the use ofembodiments of the invention in the context of optical lithography, itwill be appreciated that the invention may be used in otherapplications, for example imprint lithography, and where the contextallows, is not limited to optical lithography. In imprint lithography atopography in a patterning device defines the pattern created on asubstrate. The topography of the patterning device may be pressed into alayer of resist supplied to the substrate whereupon the resist is curedby applying electromagnetic radiation, heat, pressure or a combinationthereof. The patterning device is moved out of the resist leaving apattern in it after the resist is cured.

In the embodiments described herein, the terms “lens” and “lenselement,” where the context allows, may refer to any one or combinationof various types of optical components, comprising refractive,reflective, magnetic, electromagnetic and electrostatic opticalcomponents.

Further, the terms “radiation” and “beam” used herein encompass alltypes of electromagnetic radiation, comprising ultraviolet (UV)radiation (e.g., having a wavelength λ of 365, 248, 193, 157 or 126 nm),extreme ultra-violet (EUV or soft X-ray) radiation (e.g., having awavelength in the range of 5-20 nm, e.g., 13.5 nm), or hard X-rayworking at less than 5 nm, as well as particle beams, such as ion beamsor electron beams. Generally, radiation having wavelengths between about780-3000 nm (or larger) is considered IR radiation. UV refers toradiation with wavelengths of approximately 100-400 nm. Withinlithography, it is usually also applied to the wavelengths, which can beproduced by a mercury discharge lamp: G-line 436 nm; H-line 405 nm;and/or I-line 365 nm. Vacuum UV, or VUV (i.e., UV absorbed by air),refers to radiation having a wavelength of approximately 100-200 nm.Deep UV (DUV) generally refers to radiation having wavelengths rangingfrom 126 nm to 428 nm, and in an embodiment, an excimer laser cangenerate DUV radiation used within lithographic apparatus. It should beappreciated that radiation having a wavelength in the range of, forexample, 5-20 nm relates to radiation with a certain wavelength band, ofwhich at least part is in the range of 5-20 nm.

While specific embodiments of the invention have been described above,it will be appreciated that the invention may be practiced otherwisethan as described. For example, the invention may take the form of acomputer program containing one or more sequences of machine-readableinstructions describing a method as disclosed above, or a data storagemedium (e.g., semiconductor memory, magnetic or optical disk) havingsuch a computer program stored therein.

CONCLUSION

It is to be appreciated that the Detailed Description section, and notthe Summary and Abstract sections, is intended to be used to interpretthe claims. The Summary and Abstract sections may set forth one or morebut not all exemplary embodiments of the present invention ascontemplated by the inventor(s), and thus, are not intended to limit thepresent invention and the appended claims in any way.

The present invention has been described above with the aid offunctional building blocks illustrating the implementation of specifiedfunctions and relationships thereof. The boundaries of these functionalbuilding blocks have been arbitrarily defined herein for the convenienceof the description. Alternate boundaries can be defined so long as thespecified functions and relationships thereof are appropriatelyperformed.

The foregoing description of the specific embodiments will so fullyreveal the general nature of the invention that others can, by applyingknowledge within the skill of the art, readily modify and/or adapt forvarious applications such specific embodiments, without undueexperimentation, without departing from the general concept of thepresent invention. Therefore, such adaptations and modifications areintended to be within the meaning and range of equivalents of thedisclosed embodiments, based on the teaching and guidance presentedherein. It is to be understood that the phraseology or terminologyherein is for the purpose of description and not of limitation, suchthat the terminology or phraseology of the present specification is tobe interpreted by the skilled artisan in light of the teachings andguidance.

The breadth and scope of the present invention should not be limited byany of the above-described exemplary embodiments, but should be definedonly in accordance with the following claims and their equivalents.

1. A method comprising: forming a target on a substrate using alithographic apparatus; forming a device feature in a chip area on thesubstrate using the lithographic apparatus; determining an overlay errorof the device feature, wherein the determining the overlay error of thedevice feature comprises: measuring an overlay error of the target usingan inspection apparatus, calculating a difference between a measuredoverlay error of the target and the overlay error of the device featuredue to a characteristic of the lithographic apparatus, calculating adifference between the measured overlay error of the target and theoverlay error of the device feature due to a difference in positionbetween the target and the device feature on the substrate, andcalculating a difference between the measured overlay error of thetarget and the overlay error of the device feature due to acharacteristic of the device feature; and adjusting a parameter of thelithographic apparatus before subsequent processing on a same layer oranother layer based on the overlay error of the device feature.
 2. Themethod of claim 1, wherein the characteristic of the lithographicapparatus is an aberration.
 3. The method of claim 1, wherein thecharacteristic of the lithographic apparatus is an illumination mode ofthe lithographic apparatus.
 4. The method of claim 1, wherein thecharacteristic of the lithographic apparatus is a polarization state ofthe lithographic apparatus.
 5. The method of claim 1, wherein theinspection apparatus is integrated into the lithographic apparatus. 6.The method of claim 1, wherein the target is outside the chip area. 7.The method of claim 6, wherein the target is in a scribelane.
 8. Amethod comprising: forming a target on a substrate using a lithographicapparatus; forming a device feature in a chip area on the substrateusing the lithographic apparatus, the device feature being differentthan the target; measuring an overlay error of the target using aninspection apparatus; modeling an overlay error of the device featurebased on a measured overlay error of the target; and adjusting aparameter of the lithographic apparatus before subsequent processing ona same layer or another layer based on a modeled overlay error of thedevice feature.
 9. The method of claim 8, wherein the modeling theoverlay error of the device feature is further based on data from adatabase.
 10. The method of claim 8, wherein the modeling the overlayerror of the device feature is further based on theoretical data. 11.The method of claim 8, wherein the modeling the overlay error of thedevice feature is further based a location of the device feature on thesubstrate and a location of the target on the substrate.
 12. The methodof claim 8, wherein the modeling the overlay error of the device featureis further based a measured aberration of the lithographic apparatus.13. The method of claim 8, wherein the modeling the overlay error of thedevice feature is further based an illumination mode of the lithographicapparatus.
 14. The method of claim 8, wherein the modeling the overlayerror of the device feature is further based a polarization state of thelithographic apparatus.
 15. The method of claim 8, wherein the modelingthe overlay error of the device feature is further based acharacteristics of the device feature.
 16. The method of claim 8,wherein the modeling the overlay error of the device feature comprisesusing a model generated by measuring an overlay error of a sample devicefeature having substantially same characteristics as the device feature.17. The method of claim 8, wherein the modeling the overlay error of thedevice feature comprises simulating a relative difference between anoverlay error of the device feature and a measured overlay error of thetarget.
 18. The method of claim 8, wherein the inspection apparatus isintegrated into the lithographic apparatus.
 19. The method of claim 8,wherein the target is outside the chip area.
 20. The method of claim 19,wherein the target is in a scribelane.